1. Field of the Invention
This invention relates generally to electrochemical sensors particularly suitable for analysis of multiple chemical species in water columns and sediments, and more particularly, to a water-proof electrochemical sensor.
2. Description of the Related Art
At the surface of our planet, almost all life relies on photosynthesis—the process of using sunlight for energy to create biochemical building blocks—in one way or another. But there are places on earth that never receive sunlight, and yet life flourishes there too. Organisms that live near hydrothermal vents at depths of more than 2500 m rely not on photosynthesis, but on a totally different process called chemosynthesis. Instead of sunlight, these life forms, known as extremophiles, use the energy released from the oxidation of inorganic compounds to build biological molecules necessary for life. Chemicals such as methane, carbon dioxide, sulfur species (such as hydrogen sulfide), iron, manganese, and other trace elements affect the balance of life in this unique ecosystem.
Life has evolved at these volcanically active sites, and it is the center of great interest from biological and biotechnological points of view. Enzymes known as biocatalysts that have been isolated from hydrothermal vent bacteria can be used in the pharmaceutical and biotechnology areas instead of costly synthesized catalysts, which may be less efficient than the true biocatalysts.
The vent sites are also thought to be major contributors of inorganic elements to our oceans. Near these hot vent sites are cooler areas where diffuse vent fluids flow and in which metal sulfides accumulate to form chimney-like structures that can reach tens of meters in height. At these sites, hot hydrothermal vent fluids, 180-400+° C., are being eluted and mixed into the colder seawater, 2-4° C.
However, analyzing the environment of these vents has been a complicated challenge. In most attempts to understand the chemistry of these areas, water samples have been first collected remotely and brought to the surface for instrumental analysis. This process had been the standard for many years. The method of sample collection and the volumes of samples required depended on the types of analyses that would be used, such as atomic absorption, laser-assisted inductively coupled plasma-mass spectroscopy, and ion chemistry. Large water samples are taken from nonmetallic water sampling bottles that can be opened and closed remotely and can hold up to 2 L of water. Samples for gas analysis are taken in gas-tight syringes and sent back to the lab on land for analysis. Smaller sample collection devices are available for other types of analyses.
Although these techniques have aided the understanding of hydrothermal vents, the reduced pressure at the surface can cause outgassing of the samples, which can change their chemistry. There is, therefore, a need for an in situ analyzer that can perform analyses on samples in their respective environments to allow for a truer representation of their complex chemistry.
It is well-known to measure the concentration of various chemical and biological compounds in solution by electrochemical techniques based on oxidation-reduction processes. These techniques employ electrochemical sensors, in the nature of electrode probes. Typical electrode probes comprise gold, platinum, or carbon, and very often are combined with mercury to improve surface reproducibility.
In addition to the foregoing, iridium-based mercury electrodes, are advantageous. Examples of known iridium or mercury/iridium electrodes are found in Buffle, J. Electroanal. Chem., Vol. 216, pages 53-69 (1987); Vitre, et al., Anal. Chem. Acta, Vol. 249, pages 419-425 (1991); and U.S. Pat. No. 5,378,343. U.S. Pat. No. 5,578,178 describes a mercury drop electrode. Typical electrochemical sensors, however, are not constructed in a manner that withstands in situ use in a water column or sediment, and particularly use under sea at high temperatures and pressures.
Analytical Instrument Systems, Inc. has produced an electrochemical analyzer that allows for the real-time analysis of the above-described hydrothermal vent areas and offers a tool for the researcher to map out the centers of underwater chemical production. Using this system, a researcher can analyze, in real-time, chemical species such as oxygen, sulfide, iron sulfide, iron, and manganese. The instrument can perform all the standard types of voltammetries: sampled DC, linear sweep, cyclic, normal pulse, differential pulse, squarewave, and all the stripping analyses. The instrument can be controlled via laptop computer from shipboard or submarine, or within a research deep-submergence vehicle (DSV), such as the DSV Alvin operated out of Woods Hole (MA) Oceanographic Institution from which researchers can conduct experiments and collect samples from the floor of the ocean down to 4500 m. Due to the extreme temperature and pressure at which this probe assembly is required to operate, there is a need for an improved water-tight and heat-resistant electrochemical sensor.
It is, therefore, an object of this invention to provide a water-proof electrochemical sensor for in situ analysis of a liquid analyte.
It is another object of this invention to provide a water-proof electrochemical sensor for in situ analysis of a liquid analyte that is particularly useful a high temperatures and pressures.